1. Field of the Invention
The present invention relates to a radio channel assignment method in a mesh-like network and a recording medium of a program for controlling a radio node, and in particular to a radio channel assignment method constituted such that radio channels are assigned to respective radio links without inconsistency regardless of a topology of a network, and a recording medium of a program for controlling radio nodes.
2. Description of the Related Art
In a radio communication system having a radio network with mesh topology, a network configuration of Point-to-Point (P-P) type and Point-to-Multipoint (P-MP) type is mainly adopted.
Since a system of the P-P type is mainly used as a backbone network, it can be assumed that traffic volumes transmitted from two opposite radio stations are generally equal to each other. An FDD (Frequency Division Duplex) system which assigns different frequency bands to an incoming line and an outgoing line separately is adopted for such an assumption and easiness of frequency assignment.
In a system of the P-MP type, considering such an asymmetry that a traffic volume from a base station (BS) to a Customer Premise Equipment (CPE) is more than that in the opposite direction, a TDD (Time Division Duplex) system is adopted in which a channel assignment is made dynamically in response to the traffic volume from the BS to the CPE (for example, refer to “Performance of Dynamic Slot Assignment for Fixed Wireless Access System” by KAWABATA et. al.; IEICE Technical Report, RCS2000-78). Here, “a centralized control type dynamic channel assignment system” is adopted in which a BS controls and manages its own station and its CPEs, and the BS dynamically assigns channels to respective lines is adopted.
On the other hand, in a radio communication system of a mesh-like MP-MP type where P-P type systems are organically connected to one another, it is impractical, in view of increase in load to each radio stations, dependency to a traffic volume which instantaneously varies, scalability of network or the like, that one special station grasps traffic information to all radio stations existing in the mesh network to dynamically assign resource to them and distribute the result of the assignment to all the radio stations accurately. Therefore, “a decentralized dynamic channel assignment system” is effective in which a specific radio station does not conduct a centralized control on the other radio stations but each radio station assigns a channel to a link of its own node while acquiring information about neighbor radio stations.
Many decentralized dynamic channel assignment systems each being mainly directed to a cellular system have been proposed until now (for example, refer to JP07-212820A, JP10-285644A and JP11-18142).
However, in each of the above-described decentralized dynamic assignment systems, each BS manages assignment of radio resource such as a frequency slot or the like and evaluates channel qualities of the BS and mobile terminals existing in a coverage within the BS, and all the BSs existing in the system assign channels autonomously. For this reason, assuming that the mobile terminals are regarded as CPEs, such a system is similar to one of the P-MP type. On the other hand, when attention is paid to the BSs, the system appears to operate in a decentralized manner. However, since each BS manages terminals existing in its own coverage, the entire system is a dynamic channel assignment system of a hybrid type including the decentralized control type and the centralized control type or it is one of a semi-decentralized type, but it should not be called as one of the MP-MP type.
Further, in the above-described dynamic channel assignment system of the decentralized type, loads can be prevented from being centralized to a specific control station as compared with the dynamic channel assignment system of the centralized control type. Accordingly, a dependency to the traffic volume which varies instantaneously is improved, and even if a network is large-sized, the dynamic channel assignment system of the decentralized type can easily be applied thereto. However, in the radio communication system adopting the TDD system and utilizing a plurality of frequency slots, there are the following technical problems.
(1) In a mesh network, one node may possess a plurality of links, and a plurality of antennas and radio stations are provided for each node. When the same frequency slot is reused in the plurality of links and each link have different TDD Boundaries (transmission/reception timings), an interference through an adjacent antenna(s) in the same node can occur. Therefore, in the adjacent link, using the same frequency slot, it is necessary to make the TDD boundary common. For this reason, for each link, it is impossible to set an optimal TDD boundary according to the traffic volume of the link.
(2) When a frequency slot ID to be assigned to a link is updated, a pair of radio stations sharing the link must have a common recognition about the TDD Boundary or the frequency slot ID. Otherwise, since each node assigns different frequency slots to the same link, inconsistency occurs, which makes communication impossible.
Thus, even when the dynamic channel assignment system of the decentralized type is adopted, each node must set a combination of a frequency slot and a time slot to be assigned to its own link, that is, a radio channel considering a radio channel which has been assigned to another link. In the conventional art, however, there is not such recognition, so that it has been impossible to assign a radio channel to each link without inconsistency.
In order to solve such a technical problem, the present inventors have invented a radio channel assignment method and system in a mesh-like radio network constituted such that a radio channel is assigned to each radio link without inconsistency and in a mesh network constituting a radio mesh network where a number of radio nodes are arranged in a decentralized or distributed manner such that all closed loops constituted by a plurality of radio nodes form even polygons including each radio node as an apex thereby satisfying this condition, and a patent application for this invention (Japanese Patent Application No. 2000-149535) has been filed.
In the above-described conventional art, when a network includes an odd polygonal closed loop, there has been a problem that a topology must be modified in advance such that all closed loops are made even polygonal.